The effects of polarization and related structural parameters on the intersubband transitions of A1GaN/GaN multi- quantum wells （MQWs） have been investigated by solving the Schr6dinger and the Poisson equations self...The effects of polarization and related structural parameters on the intersubband transitions of A1GaN/GaN multi- quantum wells （MQWs） have been investigated by solving the Schr6dinger and the Poisson equations self-consistently. The results show that the intersubband absorption coefficient increases with increasing polarization while the transition wavelength decreases, which is not identical to the case of the interband transitions. Moreover, it suggests that the well width has a greater effect on the intersubband transitions than the barrier thickness, and the intersubband transition wavelength of the structure when doped in the barrier is shorter than that when doped in the well. It is found that the influences of the structural parameters differ for different electron subbands. The mechanisms responsible for these effects have been investigated in detail.展开更多
In this paper, an investigation is made on compatibility of the video formats TV (625/50/2:1/4:3), EDTV (625/50/1:1/16:9), HDTVint (1250/50/2:1/16:9) and HDTVpro(1250/50/2:1/16:9) in three-dimensional subband coding. ...In this paper, an investigation is made on compatibility of the video formats TV (625/50/2:1/4:3), EDTV (625/50/1:1/16:9), HDTVint (1250/50/2:1/16:9) and HDTVpro(1250/50/2:1/16:9) in three-dimensional subband coding. A hierarchical method is proposed leading to a more reasonable joint solution for the issues of digital transmission evolution and interlace-to-progressive scanning conversion ill the frame work of bit rate compression. Conventional HDTVint with the diamond shaped spectrum is proposed to be replaced by a kind of 'switching'HDTVin signal which consists of three components and motion detection bits (MDB). The first component and the MDB represent TV. The first plus the second component and the MDB represent EDTV.HDTVpro is splitted into switching HDTVint and extra component. The switching threshold and the length of temporal filter banks are discussed. Rearranging the pixels in subbands is recommended. Based on the proposed method, the transmission system can evolve through four steps: TV, EDTV, HDTVint and HDTVpro Results of bit rate compression are also presented. TV, EDTV, HDTVint and HDTVpro are compressed to approximately 40, 80, 128 and 256 Mbit/s respectively. Interlace scanning has drawbacks such as line flicker and line crawling as the eye follows the line structure in the picture. Progressive version switching TV and HDTVint can be reconstructed using one frame memory without the problems of handling temporal-vertical diamond shaped spectra of conventional TV and HDTVint based on a one-frame memory algorithm in the receiver.展开更多
The problem of combined radar imagery from multiple sparse frequency subbands initially incoherent to each other is of practical importance for radar target discrimination.A new coherent processing technique based on ...The problem of combined radar imagery from multiple sparse frequency subbands initially incoherent to each other is of practical importance for radar target discrimination.A new coherent processing technique based on probability density analysis of the subband data is proposed,which is applicable for radar imaging from measurements of two or more initially incoherent radar subbands.The coherence parameters for both amplitude and phase are obtained by combining modern spectral analysis with probability density estimation.The major advantage of the proposed technique lies in that it enables much more robust cohering for the sparse subband data of real-world complex targets.展开更多
This paper presents a new subband adaptive filter(SAF)algorithm for system identification scenario under impulsive interference,named generalized continuous mixed p-norm SAF(GCMPN-SAF)algorithm.The proposed algorithm ...This paper presents a new subband adaptive filter(SAF)algorithm for system identification scenario under impulsive interference,named generalized continuous mixed p-norm SAF(GCMPN-SAF)algorithm.The proposed algorithm uses a GCMPN cost function to combat the impul-sive interference.To further accelerate the convergence rate in the sparse and the block-sparse system identification processes,the proportionate versions of the proposed algorithm,the L0-norm GCMPN-SAF(L0-GCMPN-SAF)and the block-sparse GCMPN-SAF(BSGCMPN-SAF)algorithms are also developed.Moreover,the convergence analysis of the proposed algorithm is provided.Simulation results show that the proposed algorithms have a better performance than some other state-of-the-art algorithms in the literature with respect to the convergence rate and the tracking capability.展开更多
An adaptive endpoint detection algorithm based on band energy and adaptive smoothing algorithm is described. This algorithm utilizes the capability of adaptive smoothing algorithm that intensifies the discontinuity be...An adaptive endpoint detection algorithm based on band energy and adaptive smoothing algorithm is described. This algorithm utilizes the capability of adaptive smoothing algorithm that intensifies the discontinuity between local areas. The band energy features are selected because of their usefulness in detecting high energy regions (in the incoming signal) and making the distinction between speech and noise. Heuristic 'edge-focusing' is used to endpoint detection to save the time in iteration.展开更多
We develop a Monte Carlo （MC） tool incorporated with the three-subband approximation model to investigate the in-plane spln-polarized transport in GaAs/GaAlAs quantum well. Using the tool, the effects of the electro...We develop a Monte Carlo （MC） tool incorporated with the three-subband approximation model to investigate the in-plane spln-polarized transport in GaAs/GaAlAs quantum well. Using the tool, the effects of the electron occupation of higher subbands and the intersuhband scattering on the spin dephasing have been studied. Compared with the corresponding results of the simple one-snbband approximation model, the spin dephasing length is reduced four times under 0.125 kV/cm of driving electric field at 300K by the MC tool incorporated with the three-subband approximation model, indicating that the three-subbarld approximation model predicts significantly shorter spin dephasing length with temperature increasing. Our simulation results suggest that the effects of the electron occupation of higher subbands and the intersubband scattering on the spln-dependent transport of GaAs 2-dhuensional electron gas need to be considered when the driving electric field exceeds the moderate value and the lattice temperature is above 100K. The simulation by using the MC tool incorporated with the three-subband approximation model also indicates that, under a eertain driving electric field and lattice temperature, larger channel widths cause spins to be depolarized faster. Ranges of the three components of the spins are different for three different injected spin polarizations due to the anisotropy of spin-orbit interaction.展开更多
We have investigated the temperature-dependent effective mobility characteristics in impurity band and conduction subbands of n-doped silicon junctionless nanowire transistors. It is found that the electron effective ...We have investigated the temperature-dependent effective mobility characteristics in impurity band and conduction subbands of n-doped silicon junctionless nanowire transistors. It is found that the electron effective mobility of the first subband in 2-fold valleys is higher than that of the second subband in 4-fold valleys. There exists a maximum value for the effective subband mobilities at low temperatures, which is attributed to the increase of thermally activated electrons from the ionized donors in the impurity band. The experimental results indicate that the effective subband mobility is temperature-dependent on the electron interactions by thermal activation, impurity scattering, and intersubband scattering.展开更多
Image subbands can be obtained by using filterbank. Traditional compression method uses direct entropy coding for each subband. After studying the energy distribution in image subbands, we proposed a vector quantizati...Image subbands can be obtained by using filterbank. Traditional compression method uses direct entropy coding for each subband. After studying the energy distribution in image subbands, we proposed a vector quantization (VQ) coding algorithm to image subband. In the algorithm, vector quantizers were adaptively designed for high-frequency bands in an image. In particular, the edges of the image were examined and fewer bits were assigned to high-energy regions. The experimental result showed that the algorithm had higher SNR and higher compression ratio than possible by traditional subband coding, JPEG and JPEG 2000.展开更多
Electronic wave functions and energies in superlattice with a complex basis have been obtained that are more general than those of Pan et al.[Phys.Rev.B 44(1991)5668].This paper gives not only subbands but also wave f...Electronic wave functions and energies in superlattice with a complex basis have been obtained that are more general than those of Pan et al.[Phys.Rev.B 44(1991)5668].This paper gives not only subbands but also wave functions for all values of the wave number for superlattice with a complex basis.展开更多
To increase the convergence rate of the improved normalized subband adaptive filter,a simple but effective method is presented to change the reusing order of coefficient vectors of the adaptive filter. At the beginnin...To increase the convergence rate of the improved normalized subband adaptive filter,a simple but effective method is presented to change the reusing order of coefficient vectors of the adaptive filter. At the beginning of adaptation the algorithmjust uses its current coefficient vector to update the adaptive filter to maintain fast convergence rate,while in steady state it employs several most recent coefficient vectors to update the adaptive filter to reduce misalignment. Simulation results showthat the proposed algorithmcan obtain both fast convergence rate and small steady-state misalignment.展开更多
The radial contraction-expansion motion paradigm is a novel steady-state visual evoked experimental paradigm,and the electroencephalography(EEG)evoked potential is different from the traditional luminance modulation p...The radial contraction-expansion motion paradigm is a novel steady-state visual evoked experimental paradigm,and the electroencephalography(EEG)evoked potential is different from the traditional luminance modulation paradigm.The signal energy is concentrated chiefly in the fundamental frequency,while the higher harmonic power is lower.Therefore,the conventional steady-state visual evoked potential recognition algorithms optimizing multiple harmonic response components,such as the extended canonical correlation analysis(eCCA)and task-related component analysis(TRCA)algorithm,have poor recognition performance under the radial contraction-expansion motion paradigm.This paper proposes an extended binary subband canonical correlation analysis(eBSCCA)algorithm for the radial contraction-expansion motion paradigm.For the radial contraction-expansion motion paradigm,binary subband filtering was used to optimize the weighting coefficients of different frequency response signals,thereby improving the recognition performance of EEG signals.The results of offline experiments involving 13 subjects showed that the eBSCCA algorithm exhibits a better performance than the eCCA and TRCA algorithms under the stimulation of the radial contraction-expansion motion paradigm.In the online experiment,the average recognition accuracy of 13 subjects was 88.68%±6.33%,and the average information transmission rate(ITR)was 158.77±43.67 bits/min,which proved that the algorithm had good recognition effect signals evoked by the radial contraction-expansion motion paradigm.展开更多
An adaptive conjugate gradient algorithm based on subbands decomposition structure is proposed for acoustic echo cancellation in this paper. Through frequency decomposition technique and conjugate gradient algorithm, ...An adaptive conjugate gradient algorithm based on subbands decomposition structure is proposed for acoustic echo cancellation in this paper. Through frequency decomposition technique and conjugate gradient algorithm, adaptive filters operate in each decimated sub-band, This new algorithm can ensure convergence with high speed and reduce computational complexity. Simulation results indicate that the proposed algorithm demonstrates good performance for acoustic echo cancellation.展开更多
For OFDM systems with hundreds or thousands subcarriers with the adaptive bit and power loading according to each subcarrier , the signaling overhead will be awfully large. However, the adaptive bit and power loading ...For OFDM systems with hundreds or thousands subcarriers with the adaptive bit and power loading according to each subcarrier , the signaling overhead will be awfully large. However, the adaptive bit and power loading according to “subband” is an effective solution to this problem, with which the signaling overhead is expected to be dramatically decreased at the cost of some performance loss. In this paper, based on Ref . [5] but with some modification to the subband bit and power loading algorithm, we apply the algorithm to the IEEE 802.16e OFDM system. The results show that the modified subband bit and power loading algorithm can achieve better BER performance and the signaling overhead is reduced by 75% at the cost of performance loss less than 1 dB if the number of subcarriers per subband is 4 when the BER is around 10^-3.展开更多
The ultrasonic testing for the defects of complete disbond in multi-layered structure with lower acoustic impedance beneath a high acoustic impedance overburden is one of the difficult problems in ultrasonic nondestru...The ultrasonic testing for the defects of complete disbond in multi-layered structure with lower acoustic impedance beneath a high acoustic impedance overburden is one of the difficult problems in ultrasonic nondestructive testing field. A model of a multi-layered steel-rubber composite plate is depicted. Because the acoustic impedance of the steel differs far from that of the couplant water and the rubber, the energy of the signal reflected from the debonded rubber layers is very weak. More over, the flaw echoes are masked by the strong echoes reverberated in the steel plate. It's nearly impossible to identify the debonding echoes directly. The subband adaptive filtering method is discussed in the paper, where the subband decomposition is performed by mutual wavelet packets decomposition on the criterion of maximizing the cross-correlation between the signals. The simulations on both synthetic and real signals are presented. The echoes from the delaminated flaw at the depth of 5 mm in the rubber from the calculated signal, and echoes from the flaw at the depth of 3 mm from the real signal are extracted successfully.展开更多
Starting from Kane's model and taking into account the surface electron spin-orbit interaction, we have derived the dispersion relation and Landau levels of inversion layer subband on narrow-gap semiconductors. Th...Starting from Kane's model and taking into account the surface electron spin-orbit interaction, we have derived the dispersion relation and Landau levels of inversion layer subband on narrow-gap semiconductors. The capacitance-voltage spectroscopy, magnetoconductivity oscillations and cyclotron resonance spectroscopy for the p-Hg_(1-x)Cd_x Te MIS structure sample at temperature 4.2 K have been measured. From the experimental data, the subband parameters and spin-orbit coupling intensity, which are involved in the expressions of subband dispersion relation and Landau levels, have been determined. As a result, the inversion layer electron subband dispersion relation and Landau level fan chart for HgCdTe as well as the zero field spin splitting effect, the shifting and the crossing effect of Landau levels have been described quantitatively.展开更多
We propose a deterministic solver for the time-dependent multi-subband Boltzmann transport equation(MSBTE)for the two dimensional(2D)electron gas in double gate metal oxide semiconductor field effect transistors(MOSFE...We propose a deterministic solver for the time-dependent multi-subband Boltzmann transport equation(MSBTE)for the two dimensional(2D)electron gas in double gate metal oxide semiconductor field effect transistors(MOSFETs)with flared out source/drain contacts.A realistic model with six-valleys of the conduction band of silicon and both intra-valley and inter-valley phonon-electron scattering is solved.We propose a second order finite volume method based on the positive and flux conservative(PFC)method to discretize the Boltzmann transport equations(BTEs).The transport part of the BTEs is split into two problems.One is a 1D transport problem in the position space,and the other is a 2D transport problem in the wavevector space.In order to reduce the splitting error,the 2D transport problem in the wavevector space is solved directly by using the PFC method instead of splitting into two 1D problems.The solver is applied to a nanoscale double gate MOSFET and the current-voltage characteristic is investigated.Comparison of the numerical results with ballistic solutions show that the scattering influence is not ignorable even when the size of a nanoscale semiconductor device goes to the scale of the electron mean free path.展开更多
In this paper, we presented a numerical analysis of absorption coefficient, dark current and specific detectivity for InAs/GaAs quantum ring inter-subband photodetector （QRIP）. 3D SchrSdinger equation was solved usi...In this paper, we presented a numerical analysis of absorption coefficient, dark current and specific detectivity for InAs/GaAs quantum ring inter-subband photodetector （QRIP）. 3D SchrSdinger equation was solved using finite difference method and based on effective mass approximation. Dimensions of quantum ring （QR） were considered that inter-subband transition was to be accomplished for radiations of 20 μm. Resonant tunneling （RT） barriers were designed with tunneling probability of unity for electrons with energy of 0.062 meV to lower dark current of conventional QRIP. Numerical analyses show that inclusion of RT barriers can reduce dark current for about two orders of magnitude. Furthermore, specific detectivities for conventional QRIP and RToQRIP were calculated respectively, and results at different temperatures were compared. It is suggested that specific detectivity for RT-QRIP is one order of magnitude higher than that for conventional QRIP. It is suggested that RT barriers considerably improve the specific detectivity of conventional QRIP at different temperatures.展开更多
基金Project supported by the National Basic Research Program of China (Grant Nos. 2012CB619302 and 2010CB923204)the National Natural Science Foundation of China (Grant Nos. 60976042, 51002058, and 11104150)the China Postdoctoral Science Foundation (Grant No. 20100480064)
文摘The effects of polarization and related structural parameters on the intersubband transitions of A1GaN/GaN multi- quantum wells （MQWs） have been investigated by solving the Schr6dinger and the Poisson equations self-consistently. The results show that the intersubband absorption coefficient increases with increasing polarization while the transition wavelength decreases, which is not identical to the case of the interband transitions. Moreover, it suggests that the well width has a greater effect on the intersubband transitions than the barrier thickness, and the intersubband transition wavelength of the structure when doped in the barrier is shorter than that when doped in the well. It is found that the influences of the structural parameters differ for different electron subbands. The mechanisms responsible for these effects have been investigated in detail.
文摘In this paper, an investigation is made on compatibility of the video formats TV (625/50/2:1/4:3), EDTV (625/50/1:1/16:9), HDTVint (1250/50/2:1/16:9) and HDTVpro(1250/50/2:1/16:9) in three-dimensional subband coding. A hierarchical method is proposed leading to a more reasonable joint solution for the issues of digital transmission evolution and interlace-to-progressive scanning conversion ill the frame work of bit rate compression. Conventional HDTVint with the diamond shaped spectrum is proposed to be replaced by a kind of 'switching'HDTVin signal which consists of three components and motion detection bits (MDB). The first component and the MDB represent TV. The first plus the second component and the MDB represent EDTV.HDTVpro is splitted into switching HDTVint and extra component. The switching threshold and the length of temporal filter banks are discussed. Rearranging the pixels in subbands is recommended. Based on the proposed method, the transmission system can evolve through four steps: TV, EDTV, HDTVint and HDTVpro Results of bit rate compression are also presented. TV, EDTV, HDTVint and HDTVpro are compressed to approximately 40, 80, 128 and 256 Mbit/s respectively. Interlace scanning has drawbacks such as line flicker and line crawling as the eye follows the line structure in the picture. Progressive version switching TV and HDTVint can be reconstructed using one frame memory without the problems of handling temporal-vertical diamond shaped spectra of conventional TV and HDTVint based on a one-frame memory algorithm in the receiver.
文摘The problem of combined radar imagery from multiple sparse frequency subbands initially incoherent to each other is of practical importance for radar target discrimination.A new coherent processing technique based on probability density analysis of the subband data is proposed,which is applicable for radar imaging from measurements of two or more initially incoherent radar subbands.The coherence parameters for both amplitude and phase are obtained by combining modern spectral analysis with probability density estimation.The major advantage of the proposed technique lies in that it enables much more robust cohering for the sparse subband data of real-world complex targets.
文摘This paper presents a new subband adaptive filter(SAF)algorithm for system identification scenario under impulsive interference,named generalized continuous mixed p-norm SAF(GCMPN-SAF)algorithm.The proposed algorithm uses a GCMPN cost function to combat the impul-sive interference.To further accelerate the convergence rate in the sparse and the block-sparse system identification processes,the proportionate versions of the proposed algorithm,the L0-norm GCMPN-SAF(L0-GCMPN-SAF)and the block-sparse GCMPN-SAF(BSGCMPN-SAF)algorithms are also developed.Moreover,the convergence analysis of the proposed algorithm is provided.Simulation results show that the proposed algorithms have a better performance than some other state-of-the-art algorithms in the literature with respect to the convergence rate and the tracking capability.
文摘An adaptive endpoint detection algorithm based on band energy and adaptive smoothing algorithm is described. This algorithm utilizes the capability of adaptive smoothing algorithm that intensifies the discontinuity between local areas. The band energy features are selected because of their usefulness in detecting high energy regions (in the incoming signal) and making the distinction between speech and noise. Heuristic 'edge-focusing' is used to endpoint detection to save the time in iteration.
基金Project supported in part by the National Natural Science Foundation of China （Grant Nos 90307006 and 10234010）, and the Research Fund for the Datoral Program of Higher Education of China （Grant Nos 20040001026 and 20020001018）.
文摘We develop a Monte Carlo （MC） tool incorporated with the three-subband approximation model to investigate the in-plane spln-polarized transport in GaAs/GaAlAs quantum well. Using the tool, the effects of the electron occupation of higher subbands and the intersuhband scattering on the spin dephasing have been studied. Compared with the corresponding results of the simple one-snbband approximation model, the spin dephasing length is reduced four times under 0.125 kV/cm of driving electric field at 300K by the MC tool incorporated with the three-subband approximation model, indicating that the three-subbarld approximation model predicts significantly shorter spin dephasing length with temperature increasing. Our simulation results suggest that the effects of the electron occupation of higher subbands and the intersubband scattering on the spln-dependent transport of GaAs 2-dhuensional electron gas need to be considered when the driving electric field exceeds the moderate value and the lattice temperature is above 100K. The simulation by using the MC tool incorporated with the three-subband approximation model also indicates that, under a eertain driving electric field and lattice temperature, larger channel widths cause spins to be depolarized faster. Ranges of the three components of the spins are different for three different injected spin polarizations due to the anisotropy of spin-orbit interaction.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0200503)
文摘We have investigated the temperature-dependent effective mobility characteristics in impurity band and conduction subbands of n-doped silicon junctionless nanowire transistors. It is found that the electron effective mobility of the first subband in 2-fold valleys is higher than that of the second subband in 4-fold valleys. There exists a maximum value for the effective subband mobilities at low temperatures, which is attributed to the increase of thermally activated electrons from the ionized donors in the impurity band. The experimental results indicate that the effective subband mobility is temperature-dependent on the electron interactions by thermal activation, impurity scattering, and intersubband scattering.
文摘Image subbands can be obtained by using filterbank. Traditional compression method uses direct entropy coding for each subband. After studying the energy distribution in image subbands, we proposed a vector quantization (VQ) coding algorithm to image subband. In the algorithm, vector quantizers were adaptively designed for high-frequency bands in an image. In particular, the edges of the image were examined and fewer bits were assigned to high-energy regions. The experimental result showed that the algorithm had higher SNR and higher compression ratio than possible by traditional subband coding, JPEG and JPEG 2000.
文摘Electronic wave functions and energies in superlattice with a complex basis have been obtained that are more general than those of Pan et al.[Phys.Rev.B 44(1991)5668].This paper gives not only subbands but also wave functions for all values of the wave number for superlattice with a complex basis.
基金Supported by the National Natural Science Foundation of China( 61471251 61101217)the Natural Science Foundation of Jiangsu Province of China (BK20131164)
文摘To increase the convergence rate of the improved normalized subband adaptive filter,a simple but effective method is presented to change the reusing order of coefficient vectors of the adaptive filter. At the beginning of adaptation the algorithmjust uses its current coefficient vector to update the adaptive filter to maintain fast convergence rate,while in steady state it employs several most recent coefficient vectors to update the adaptive filter to reduce misalignment. Simulation results showthat the proposed algorithmcan obtain both fast convergence rate and small steady-state misalignment.
基金This work is granted by National Natural Science Foundation of China(Grant Nos.62006024,62071057)the Fundamental Research Funds for the Central Universities(BUPT Project No.2019XD17)Aeronautical Science Foundation of China(NO.2019ZG073001).
文摘The radial contraction-expansion motion paradigm is a novel steady-state visual evoked experimental paradigm,and the electroencephalography(EEG)evoked potential is different from the traditional luminance modulation paradigm.The signal energy is concentrated chiefly in the fundamental frequency,while the higher harmonic power is lower.Therefore,the conventional steady-state visual evoked potential recognition algorithms optimizing multiple harmonic response components,such as the extended canonical correlation analysis(eCCA)and task-related component analysis(TRCA)algorithm,have poor recognition performance under the radial contraction-expansion motion paradigm.This paper proposes an extended binary subband canonical correlation analysis(eBSCCA)algorithm for the radial contraction-expansion motion paradigm.For the radial contraction-expansion motion paradigm,binary subband filtering was used to optimize the weighting coefficients of different frequency response signals,thereby improving the recognition performance of EEG signals.The results of offline experiments involving 13 subjects showed that the eBSCCA algorithm exhibits a better performance than the eCCA and TRCA algorithms under the stimulation of the radial contraction-expansion motion paradigm.In the online experiment,the average recognition accuracy of 13 subjects was 88.68%±6.33%,and the average information transmission rate(ITR)was 158.77±43.67 bits/min,which proved that the algorithm had good recognition effect signals evoked by the radial contraction-expansion motion paradigm.
文摘An adaptive conjugate gradient algorithm based on subbands decomposition structure is proposed for acoustic echo cancellation in this paper. Through frequency decomposition technique and conjugate gradient algorithm, adaptive filters operate in each decimated sub-band, This new algorithm can ensure convergence with high speed and reduce computational complexity. Simulation results indicate that the proposed algorithm demonstrates good performance for acoustic echo cancellation.
文摘For OFDM systems with hundreds or thousands subcarriers with the adaptive bit and power loading according to each subcarrier , the signaling overhead will be awfully large. However, the adaptive bit and power loading according to “subband” is an effective solution to this problem, with which the signaling overhead is expected to be dramatically decreased at the cost of some performance loss. In this paper, based on Ref . [5] but with some modification to the subband bit and power loading algorithm, we apply the algorithm to the IEEE 802.16e OFDM system. The results show that the modified subband bit and power loading algorithm can achieve better BER performance and the signaling overhead is reduced by 75% at the cost of performance loss less than 1 dB if the number of subcarriers per subband is 4 when the BER is around 10^-3.
基金This work was supported by the National Science Foundation of China (No. 19974063) and the President Foundation of the Institute of Acoustics, Chinese Academy of Sciences.
文摘The ultrasonic testing for the defects of complete disbond in multi-layered structure with lower acoustic impedance beneath a high acoustic impedance overburden is one of the difficult problems in ultrasonic nondestructive testing field. A model of a multi-layered steel-rubber composite plate is depicted. Because the acoustic impedance of the steel differs far from that of the couplant water and the rubber, the energy of the signal reflected from the debonded rubber layers is very weak. More over, the flaw echoes are masked by the strong echoes reverberated in the steel plate. It's nearly impossible to identify the debonding echoes directly. The subband adaptive filtering method is discussed in the paper, where the subband decomposition is performed by mutual wavelet packets decomposition on the criterion of maximizing the cross-correlation between the signals. The simulations on both synthetic and real signals are presented. The echoes from the delaminated flaw at the depth of 5 mm in the rubber from the calculated signal, and echoes from the flaw at the depth of 3 mm from the real signal are extracted successfully.
基金Project partly supported by the National Natural Science Foundation of China and partly by the A. V. Humboldt Foundation in F. R. Germany.
文摘Starting from Kane's model and taking into account the surface electron spin-orbit interaction, we have derived the dispersion relation and Landau levels of inversion layer subband on narrow-gap semiconductors. The capacitance-voltage spectroscopy, magnetoconductivity oscillations and cyclotron resonance spectroscopy for the p-Hg_(1-x)Cd_x Te MIS structure sample at temperature 4.2 K have been measured. From the experimental data, the subband parameters and spin-orbit coupling intensity, which are involved in the expressions of subband dispersion relation and Landau levels, have been determined. As a result, the inversion layer electron subband dispersion relation and Landau level fan chart for HgCdTe as well as the zero field spin splitting effect, the shifting and the crossing effect of Landau levels have been described quantitatively.
基金supported by the NKBRP(Grants 2006CB302705,2005CB321704)the NSFC(Grants 10701005,11011130029)sponsored by SRF for ROCS,SEM.
文摘We propose a deterministic solver for the time-dependent multi-subband Boltzmann transport equation(MSBTE)for the two dimensional(2D)electron gas in double gate metal oxide semiconductor field effect transistors(MOSFETs)with flared out source/drain contacts.A realistic model with six-valleys of the conduction band of silicon and both intra-valley and inter-valley phonon-electron scattering is solved.We propose a second order finite volume method based on the positive and flux conservative(PFC)method to discretize the Boltzmann transport equations(BTEs).The transport part of the BTEs is split into two problems.One is a 1D transport problem in the position space,and the other is a 2D transport problem in the wavevector space.In order to reduce the splitting error,the 2D transport problem in the wavevector space is solved directly by using the PFC method instead of splitting into two 1D problems.The solver is applied to a nanoscale double gate MOSFET and the current-voltage characteristic is investigated.Comparison of the numerical results with ballistic solutions show that the scattering influence is not ignorable even when the size of a nanoscale semiconductor device goes to the scale of the electron mean free path.
文摘In this paper, we presented a numerical analysis of absorption coefficient, dark current and specific detectivity for InAs/GaAs quantum ring inter-subband photodetector （QRIP）. 3D SchrSdinger equation was solved using finite difference method and based on effective mass approximation. Dimensions of quantum ring （QR） were considered that inter-subband transition was to be accomplished for radiations of 20 μm. Resonant tunneling （RT） barriers were designed with tunneling probability of unity for electrons with energy of 0.062 meV to lower dark current of conventional QRIP. Numerical analyses show that inclusion of RT barriers can reduce dark current for about two orders of magnitude. Furthermore, specific detectivities for conventional QRIP and RToQRIP were calculated respectively, and results at different temperatures were compared. It is suggested that specific detectivity for RT-QRIP is one order of magnitude higher than that for conventional QRIP. It is suggested that RT barriers considerably improve the specific detectivity of conventional QRIP at different temperatures.
